The present invention relates to a method and means for enhancing the performance and efficiency of water turbines, in particular, but not exclusively, Pelton turbines.
Generally, when water at high pressure and/or velocity hits the parts of the turbine intended to be rotated, water has a tendency to splash, causing spray on the casing walls and/or on other parts of the turbine intended to be rotated. In particular, Pelton turbines are exposed to secondary losses originating from water of high velocity leaving the buckets, hitting stationary parts inside of the turbine casing and causing losses generated from                i) splash back to the wheel and        ii) disturbances to the incoming jet of water.        
Pelton turbines with wheels having a horizontal axis of rotation are in particular exposed to such losses. Such vagrant spray is detrimental and should be eliminated, or at least reduced.
Further, when water subjected to high pressure hits hard surfaces and obstructions at an angle, the water has a tendency to be highly pulverized, causing fine droplets and droplets of “compressed” mist inside the housing. Such droplets or mist of “compressed” droplets is another source of loss in a water turbine, causing so called “windage loss”. “Windage loss” in a Pelton turbine comprises frictional losses and impact losses between rotating parts (running wheel) and particles in the atmosphere inside the casing surrounding the rotating parts. For a Pelton turbine, this means the rotational resistance which the wheel is subjected to inside the casing, caused by air containing “compressed” water droplets.
It has previously been proposed to keep vagrant water spray away from the turbine wheel and buckets on a Pelton turbine. In order to reduce vagrant spray on the rotating wheel and the buckets in a Pelton turbine having a horizontal axis of rotation, it has been proposed to provide the upper region of a turbine casing with vertical metal sheets parallel to the plane of the turbine wheel, while horizontal sheets are disposed opposite the high pressure nozzle in order to prevent water spray from reaching the upper region of the casing.
U.S. Pat. No. 4,950,130 discloses a Pelton turbine which includes a wheel disc with buckets, mounted within a casing on a rotatable shaft. At least one nozzle is provided for expelling a fluid jet tangentially of the disc onto the buckets. A partition divides the interior of the housing into a spray fluid and outlet region and an upper ventilation region. The partition is located so that more than half the turbine wheel rotates in the relatively dry ventilation region. The driving fluid falls from the buckets into a sump in the outlet region, while residual fluid is wiped off the turbine wheel by the partition. The ventilation region allows ventilation of the casing and also produces a flow of gas for increasing the pressure in the sump to improve outflow of fluid.
Internal flow observations by model testing of Pelton turbines reveal the existence of the physical loss phenomena due to internal water flow interactions inside the turbine casing. Development and design of flow guides by model testing is a common way to solve the problem. However, the process can be very time consuming, and sometimes gives only minor efficiency improvement.
Previous and existing approach to the problem of energy losses due to energy dissipation in water turbines due to splashing water, is to design and provide the turbine casing with physical flow guides and screens as described above. It is found by model testing, however, that even if flow guides are installed, only a minor part of the losses may be eliminated.
Applicants have developed enhancements intended to improve the performance, reliability and the efficiency of a water turbine.
The devices and methods disclosed herein may be applied to reduce the required size and volume of the turbine casing.
The devices and methods disclosed herein may be applied to provide a solution which may also be applied to existing turbines, thereby improving their efficiency and performance in a low cost manner.
The devices and methods disclosed herein may be applied to prevent vagrant water or secondary spray of water from hitting the rotating parts of the turbine.
The devices and methods disclosed herein may be applied to improve the atmospheric conditions inside the turbine casing, reducing the “windage losses”.
The devices and methods disclosed herein may be applied to reduce vibration and noise originating from the turbine casing walls being exposed to water of high velocities and high frequency turbulences.
The devices and methods disclosed herein may be applied to eliminate or reduce secondary losses occurring inside a water turbine is provided.
The devices and methods disclosed herein may be used to enhance the efficiency and the performance of water turbines in general, and on Pelton turbines in particular, by attaching one or more energy damping devices on stationary, water splash exposed parts inside the turbine casing in order to reduce the amount of detrimental spray water on the rotating turbine wheel, thereby dissipating energy at least from water of high velocity leaving the buckets and/or from dense pulverized water mist.
It is feasible to enhance the efficiency and the performance of existing water turbines to include the devices disclosed herein without having to perform extensive and expensive re-construction or up-grading of existing turbines.
By covering the exposed walls and other stationary parts inside the turbine casing with the energy dissipating device, the energy that always is left in the water will be dampened out and the water will fall down without causing any negative effects. For new Pelton turbines, energy dissipating wall covers make it possible to reduce the main casing dimensions and to simplify the casing design, and still maintain a high level of performance. For upgrading of old, existing turbines, wall covers, if needed, may compensate for more costly introduction of flow guides and screens, for example of the guiding ribs type or the like.
Secondary efficiency losses may vary from 0.5% for new turbines, to 1-5% or more for old, existing turbines. Eliminating these losses will
1) improve the efficiency of the turbine,
2) increase reliability regarding given guarantees and
3) reduce production costs for high performance Pelton turbines.
Although production costs will increase somewhat due to the addition of the wall covers, the energy generation of the power plant in which the turbine is installed will increase due to increased efficiency, making such investment payable.
One embodiment of the proposed device may preferably be in the form of a simple, low-cost, standardized mat of a certain shape, width and thickness, preferably made from commercial materials. The mat is rolled out, trimmed to the actual wall or part dimension, and fixed to the walls. In addition to efficiency improvement, the mat also has a potential to reduce forces acting on stationary turbine parts at runaway conditions.
Atmospheric conditions inside the turbine casing may be improved using the devices and methods disclosed herein, causing reduction of the “windage losses”, since the turbine casing walls being hit by water from the wheel buckets are covered by means for absorbing, dampening or dissipating energy.
Further, due to said means for absorbing, dampening or dissipating, the vibration and noise originating from the turbine casing exposed to water of high velocities and frequencies are reduced.
According to the present invention the detrimental effect of “aggressive” water is dampened by limiting detrimental back spray of water on to the running wheel and/or the water jet(s) leaving the water nozzles. Further, the so called “windage loss” is reduced.